The formation, maturation, and function of synapses requires the exquisite coordination of transynaptic adhesion complexes, enabling the concentration and control of pre- and postsynaptic signaling machinery. In particular, the association of presynaptic neurexins (Nrxns) with their postsynaptic ligands (e.g. neuroligins, LRRTMs, etc.), mediates several aspects of synaptic function, such as synaptic transmission and the assembly of functional postsynaptic sites. A growing body of genetic evidence implicates heterozygous deletions of the gene encoding Nrxn-1 in the pathoetiology of idiopathic autism spectrum disorders and schizophrenia. Still very little is known regarding the function and regulation of Nrxn-1 at developing and adult synapses, an understanding of which may improve our knowledge of neurodevelopmental disorders and reveal novel pharmacological targets. I present here preliminary data that validates the use of two new mouse models for studying Nrxn-1, including a Nrxn-1-HA knockin mouse which will allow improved detection of endogenous Nrxn-1, as well as a Nrxn-1?/? conditional knockout mouse (cKO) mouse for functional studies. Using the Nrxn-1-HA knockin, I further show that synaptic activity influences the processing of Nrxn-1 in a metalloproteinase-dependent fashion, which may represent an important regulatory mechanism of Nrxn- containing adhesion complexes. In order to better understand the basic function and regulation of Nrxn-1 at synapses, I propose to identify the specific metalloproteinase and cleavage site responsible for activity- dependent Nrxn-1 processing. Then I will determine, in parallel, the basic function of Nrxn-1 in regulating the formation and physiological function of hippocampal synapses. Finally, through a series of rescue experiments achieved through lentiviral re-expression of wild-type, cleavage-resistant, and cleavage-inducible Nrxn-1? in Nrxn-1?/? cKO neurons, I will assess the role of Nrxn-1 processing in its normal function. It is anticipated that the proposed research will provide fundamental insight into how Nrxn-1 deletions give rise to human neurodevelopmental disorders and will offer the first functional analysis of extracellular proteolysis as a regulatory mechanism of neurexin-containing adhesion complexes.